Process for silicon nitride removal selective to SiGex

ABSTRACT

A method for selectively removing silicon nitride is described. In particular, the method includes providing a substrate having a surface with silicon nitride exposed on at least one portion of the surface and SiGe x  (x is greater than or equal to zero) exposed on at least another portion of the surface, and dispensing an oxidizing agent onto the surface of the substrate to oxidize the exposed SiGe x . Thereafter, the method includes dispensing a silicon nitride etching agent as a liquid stream onto the surface of the substrate to remove at least a portion of the silicon nitride.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of pending U.S. patentapplication Ser. No. 13/312,148, entitled “PROCESS FOR SELECTIVELYREMOVING NITRIDE FROM SUBSTRATES” (TEF-142US1), published as U.S. PatentApplication Publication Ser. No. 2012/0145672, and filed on Dec. 6,2011. The entire content of this application is herein incorporated byreference. U.S. patent application Ser. No. 13/312,148 in turn claimspriority to U.S. patent application Ser. No. 61/421,808, filed on Dec.10, 2010.

BACKGROUND OF THE INVENTION

1. Field of Invention

The invention relates to a method for removing material from asubstrate, and in particular, a method for selectively removing siliconnitride from a substrate.

2. Description of Related Art

Typically, during fabrication of integrated circuits (ICs),semiconductor production equipment utilize a (wet) etching or cleaningprocess to remove or etch material from target locations on asemiconductor substrate. The success of the etching process requires anetching chemistry that includes chemical reactants suitable forselectively removing one material while substantially not removinganother material. Various compositions have been developed for removalof specific classes of materials from substrates in semiconductor wafertechnologies.

For example, silicon nitride is commonly used in semiconductorprocessing as a cap layer, spacer layer, or hard mask layer, to name afew, during the formation of various devices. In these processingtechniques, at least a portion of the silicon nitride layer isselectively removed via an etching process. In particular, the siliconnitride layer is selectively removed relative to silicon oxide. Onetechnique includes submersing the substrate comprising silicon nitridein a bath of boiling H₃PO₄, which has been shown to achieve aselectivity of about 35:1 for etching silicon nitride relative tosilicon dioxide.

However, even with this success, it remains desirable to identifyalternative techniques and compositions for treatment of substrates,particularly to remove nitride materials, especially silicon nitride,from substrates such as semiconductor wafers with selectivity to, forexample, silicon and silicon-germanium alloys.

SUMMARY OF THE INVENTION

Embodiments of the invention relate to a method for removing materialfrom a substrate, and in particular, a method for selectively removingsilicon nitride from a substrate.

According to one embodiment, a method for selectively removing siliconnitride is described. In particular, the method includes providing asubstrate having a surface with silicon nitride exposed on at least oneportion of the surface and SiGe_(x), wherein x is greater than or equalto zero, exposed on at least another portion of the surface, anddispensing an oxidizing agent onto the surface of the substrate tooxidize the exposed SiGe_(x). Thereafter, the method includes dispensinga silicon nitride etching agent as a liquid stream onto the surface ofthe substrate to remove at least a portion of the silicon nitride.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIGS. 1A through 1C depict a semiconductor device;

FIG. 2 illustrates a method for selectively removing silicon nitrideaccording to an embodiment;

FIG. 3 is a schematic diagram of an apparatus that can carry out anembodiment of the process of the present invention;

FIG. 4 is a cross sectional view of a spray bar for carrying out anembodiment of the process of the present invention; and

FIG. 5 is a schematic diagram of an apparatus that can carry out anembodiment of the process of the present invention.

DETAILED DESCRIPTION OF SEVERAL EMBODIMENTS

Methods for selectively removing material from a substrate are describedin various embodiments. One skilled in the relevant art will recognizethat the various embodiments may be practiced without one or more of thespecific details, or with other replacement and/or additional methods,materials, or components. In other instances, well-known structures,materials, or operations are not shown or described in detail to avoidobscuring aspects of various embodiments of the invention. Similarly,for purposes of explanation, specific numbers, materials, andconfigurations are set forth in order to provide a thoroughunderstanding of the invention. Nevertheless, the invention may bepracticed without specific details. Furthermore, it is understood thatthe various embodiments shown in the figures are illustrativerepresentations and are not necessarily drawn to scale.

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structure, material, orcharacteristic described in connection with the embodiment is includedin at least one embodiment of the invention, but do not denote that theyare present in every embodiment. Thus, the appearances of the phrases“in one embodiment” or “in an embodiment” in various places throughoutthis specification are not necessarily referring to the same embodimentof the invention. Furthermore, the particular features, structures,materials, or characteristics may be combined in any suitable manner inone or more embodiments. Various additional layers and/or structures maybe included and/or described features may be omitted in otherembodiments.

“Substrate” as used herein generically refers to the object beingprocessed in accordance with the invention. The substrate may includeany material portion or structure of a device, particularly asemiconductor or other electronics device, and may, for example, be abase substrate structure, such as a semiconductor wafer or a layer on oroverlying a base substrate structure such as a thin film. Thus,substrate is not intended to be limited to any particular basestructure, underlying layer or overlying layer, patterned orunpatterned, but rather, is contemplated to include any such layer orbase structure, and any combination of layers and/or base structures.The description below may reference particular types of substrates, butthis is for illustrative purposes only and not limitation.

As noted above, removal processes, such as etching and cleaning, for usein semiconductor device manufacturing require chemical compositions thatachieve selectivity of one material relative to another material, i.e.,one material is selectively removed while another material remainssubstantially unaffected. FIG. 1A depicts a schematic cross-section of asemiconductor device 1, such as a gate structure.

The semiconductor device 1 includes substrate 2, such as amonocrystalline Si substrate, a SiGe_(x) region 3 (wherein x is greaterthan or equal to 0), and an isolation region 5. The SiGe_(x) region 3may include Si, Ge, or SiGe alloy. The isolation region 3 may includesilicon oxide (SiO_(y), wherein y is greater than or equal to 0). Thesemiconductor device 1 further includes a gate region having gate 4,gate dielectric and spacer 8, gate cap layer 7, silicon nitride layer 6,and silicon oxide layer 9.

At this intermediate stage of fabrication, the silicon nitride layer 6is exposed, and it is necessary to preferentially remove the siliconnitride layer 6 from the substrate relative to other materials beingretained on the substrate, such as SiGe_(x) region 3 and silicon oxidelayer 9. With conventional removal processes, the silicon nitride layer6 may be removed, but at the expense of removing the SiGe_(x) region 3,which is unacceptable (see FIG. 1B). As shown in FIG. 1C, the siliconnitride layer 6 must be removed without removing the SiGe_(x) region 3.

Therefore, according to an embodiment, a method of removing the siliconnitride layer 6 with selectivity to the SiGe_(x) region 3 is describedaccording to various embodiments. Referring now to FIG. 3, a method forselectively removing silicon nitride is illustrated according to anembodiment. The method includes a flow chart 10 beginning in 11 withproviding a substrate having a surface with silicon nitride exposed onat least one portion of the surface and SiGe_(x), wherein x is greaterthan or equal to zero, exposed on at least another portion of thesurface. The SiGe_(x) may include Si, Ge, or SiGe alloy.

In 12, an oxidizing agent is dispensed onto the surface of the substrateto oxidize the exposed SiGe_(x). In one example, the dispensing of theoxidizing agent may include exposing the substrate to a mixturecontaining sulfuric acid and hydrogen peroxide. The sulfuric acid may beheated to a temperature in excess of 150 degrees C., or alternatively,to a temperature in excess of 200 degrees C. Furthermore, water, such assteam, may be added to the mixture of sulfuric acid and hydrogenperoxide. Other oxidizing agents are also contemplated. For instance,the oxidizing agent may include a peroxide, such as hydrogen peroxide,or other oxidizing media, e.g., ozone or aqueous ozone.

In another example, the dispensing of the oxidizing agent may includeexposing the substrate to a mixture containing sulfuric acid andhydrogen peroxide in the presence of water vapor. The mixture containingsulfuric acid and hydrogen peroxide may be dispensed from a first arrayof injection openings located above the substrate, and the water vapormay be dispensed from a second array of openings. Additionally, thefirst array of openings and the second array of openings may be orientedrelative to one another to allow the mixture of sulfuric acid andhydrogen peroxide and the water vapor to mix in a space above thesubstrate. Furthermore, the first array of openings and the second arrayof openings may be distributed radially along a spray arm that extendsabove the substrate from approximately a central region of the substrateto approximately a peripheral region of the substrate. Further yet, thesubstrate may be rotated while dispensing the mixture of sulfuric acidand hydrogen peroxide and the water vapor.

In 13, a silicon nitride etching agent is dispensed as a liquid streamonto the surface of the substrate to remove at least a portion of thesilicon nitride, following the dispensing of the oxidizing agent. Thedispensing of a silicon nitride etching agent may comprise dispensingsulfuric acid, or phosphoric acid, or both sulfuric and phosphoric acid.For instance, the dispensing of a silicon nitride etching agent maycomprise dispensing phosphoric acid and sulfuric acid onto the surfaceof the substrate as a mixed acid liquid stream at a temperature greaterthan about 150 degrees C. Water may be added to a liquid solution of themixed acid liquid stream as or after the liquid solution of the mixedacid liquid stream passes through a nozzle. Furthermore, the substratemay be rotated during the dispensing of the mixed acid stream.

The mixed acid liquid stream may be flowed onto the substrate in theform of a continuous stream or may be sprayed onto the substrate in theform of liquid aerosol droplets. In one example, the phosphoric acid andsulfuric acid are mixed in a vessel for storage prior to dispensing froma nozzle as the mixed acid liquid stream. In another example, thephosphoric acid and sulfuric acid are mixed in-line at a locationupstream from a nozzle to form the mixed acid liquid stream, or thephosphoric acid and sulfuric acid are mixed in a nozzle assembly priorto being ejected from a nozzle as the mixed acid liquid stream. In yetanother example, the phosphoric acid and sulfuric acid are dispensed asseparate liquid solutions in the form of streams from separate orificesof a nozzle assembly, which separate streams then impinge and form themixed acid liquid stream externally of the nozzle and prior to contactwith the surface of the substrate.

The constituents of the mixed acid liquid stream can be heated to thedesired application temperature at any desired location in thedispensing process. For example, the constituents can be individuallypreheated and then mixed, or can be mixed and then heated to the desiredtemperature. The constituents can be heated in bulk, or in the processline in an on-demand basis.

In one embodiment, the mixed acid liquid stream is prepared by mixing aphosphoric acid solution that is at least about 80% by weight phosphoricacid with a sulfuric acid solution that is at least about 90% by weightsulfuric acid in a volume ratio of phosphoric acid to sulfuric acid thatlies within the range from 3:1 to 1:6. In another embodiment, thephosphoric acid solution is 85% (by weight) phosphoric acid and thesulfuric acid solution is 98% (by weight) sulfuric acid. In anotherembodiment, the volume ratio of phosphoric acid to sulfuric acid lieswithin the range of 1:2 to 1:4.

In a preferred embodiment, the liquid sulfuric acid solution has awater/sulfuric acid molar ratio of no greater than about 5:1. Thus, theliquid sulfuric acid solution is limited in water content. In oneembodiment, the liquid sulfuric acid solution may comprise a solventthat does not substantially interfere with the coordination ofsubsequently added water (and preferably water vapor) with sulfuricacid, as discussed in more detail herein. Preferred solvents may includeinert materials with respect to the substrate to be treated (e.g., thesubstrate), such as fluorine based liquids. One example of an inertsolvent includes a solvent selected from the FLUORINERT™ solvent family,commercially available from 3M (St. Paul, Minn.).

It should be noted that the above mentioned molar ratio recites thewater/sulfuric acid molar ratio, and not the solvent/sulfuric acidratio. This underscores the significance of the criterion that thesolvent that does not substantially interfere with the coordination ofsubsequently added water with sulfuric acid and does not factor intothis ratio. More preferably, the liquid sulfuric acid composition may behighly concentrated. Preferably, the liquid sulfuric acid solution isdispensed at a sulfuric acid concentration of at least about 80 v/v %,more preferably at least about 90 v/v %, and most preferably at leastabout 94 v/v %.

Water may be added to a liquid solution of the mixed acid liquid streamas or after the liquid solution of the mixed acid liquid stream passesthrough a nozzle. It has been found that addition of water to the systemimmediately prior to application of the mixed acid liquid stream to thesubstrate provides a number of benefits. First, the mixed acid liquidstream may be readily heated to a higher temperature than more dilutesolutions having water added at an earlier stage. The reason is theboiling point of concentrated acid is higher than the boiling point of adiluted acid. Additionally, when the liquid water is added toconcentrated sulfuric acid, in particular, the resulting mixture isbeneficially heated in the mixing process by the heat of mixing of thesesolutions.

A particular advantage exists when water is added as water vapor orsteam. Water vapor has more energy in the vapor-phase than in the liquidphase, which corresponds roughly to the heat of vaporization stored inthe water vapor. While not being bound by theory, water vapor mayadditionally be in a more reactive state relative to silicon nitridethan water in the liquid state or at a lower temperature. While stillnot being bound by theory, it is further believed that the concentratedliquid sulfuric acid composition of the mixed acid liquid stream has adesiccating effect, thereby causing water from the water vapor to becondensed into the mixed acid liquid stream and releasing the energycorresponding roughly to the heat of vaporization stored in the watervapor.

For purposes of the present invention, water vapor is defined as waterin the gaseous form, and distinguished from small droplets of watercommonly called “mist.” Because mist is water that is condensed in theform of small droplets, there is essentially no net warming effect whenmist settles on a surface that would correspond to a heat ofvaporization. For purposes of the present invention, steam is vaporizedwater at or above the boiling point of water, which depends on thepressure, e.g. 100 degrees C. if the pressure is 1 atmosphere. Whensteam is provided at a temperature greater than the boiling point ofwater, is it called superheated steam. Water vapor optionally may beprovided from compositions comprising ingredients in addition to water,such as dissolved gasses (e.g., nitrogen). It is contemplated that watervapor may be supplied in any manner, either essentially pure, or incompositions, either above, or below or at 100 degrees C., and havingpressures or partial pressures of water vapor either above, below, or at1 atm.

It has been found that mixing, in particular, a concentrated sulfuricacid solution with a water-containing solution, as described above, isan exothermic interaction, liberating heat energy. It, therefore, isadvantageous to mix these solutions immediately prior to application ofthe mixed acid liquid stream to the substrate in order to utilize thisextra energy and promote a higher etch rate. Also, this exothermiceffect may allow the liquid acid solutions to be heated to a lowerinitial temperature, such as 150 degrees C., before mixing with wateror, in particular, steam. In addition, treating the substrate with thischemical mixture in the presence of steam or water vapor, orsimultaneously dispensing steam or water vapor while pouring ordispensing the chemical mixture may provide additional temperatureincrease as it is expected that the dissolution of steam into the mixedacid liquid stream having a high concentration of sulfuric acid willproduce an additional exotherm, or release of energy.

In other embodiments, the silicon nitride etching agent may include HF,such as dilute, heated HF at temperatures in excess of 100 degrees C.and dilution ratios to water of order 8000:1. In yet other embodiments,the silicon nitride etching agent may include phosphoric acid andvarious additives, such as NH₄F (ammonium fluoride), NH₄HF₂ (ammoniumhydrogen difluoride), HF, Si(OH)₄ (silicic acid, or more generally[SiO_(a)(OH)_(4-2a)]_(b), wherein a and b are integers), TEOS(tetraethyl orthosilicate), to name a few.

In some cases, the inventors have observed the process to exhibitexcellent selectivity of silicon nitride etch as compared to silicide,monocrystalline silicon, polycrystalline silicon, silicon-germaniumalloys, and silicon oxide. The method for selectively etching siliconnitride described above may be observed a wide range of temperature, andtherefore, it may advantageously permit selective etching at relativelylow processing temperature (i.e., from about 150 degrees C. to about 180degrees C.). The ability to provide selective etching at such processingtemperatures is advantageous for certain substrates, device parameters,or tool set-ups in which the use of higher temperature conditions isundesirable. However, nitride etch enhancement effect is more pronouncedat a temperature greater than or equal to about 180 degrees C., morepreferably at a temperature greater than about 200 degrees C., andpreferably at a temperature in the range of about 190 degrees C. toabout 240 degrees C.

Therefore, according to another embodiment, prior to dispensing thesilicon nitride etching agent, a heating agent may be dispensed onto thesurface of the substrate to pre-heat the substrate to a targettemperature. The target temperature may exceed 150 degrees C.Furthermore, the dispensing of the oxidizing agent and dispensing of theheating agent may be performed simultaneously or overlapping oneanother.

According to yet another embodiment, the dispensing of an oxidizingagent onto the surface of the substrate and the dispensing of a siliconnitride etching agent as a liquid stream onto the surface of thesubstrate may be repeated two or more cycles to selectively remove atarget amount of the silicon nitride.

As described above, the selective removal of silicon nitride relative toexposed SiGe_(x) is carried out by dispensing an oxidizing agent onto asurface of the substrate to oxidize exposed SiGe_(x). Thereafter, asilicon nitride etching agent may be used to selectively remove thesilicon nitride relative to the oxidized silicon surfaces. FIGS. 3through 5 describe an apparatus for carrying out the method forselectively removing silicon nitride according to several embodiments.

FIG. 3 shows a modified spray processing system 110 for carrying out thepresent invention. In system 110, wafer 113, as a particularmicroelectronic device for example, is supported on a rotatable chuck114 that is driven by a spin motor 115. This portion of system 110corresponds to a conventional spray processor device. Spray processorshave generally been known, and provide an ability to remove liquids withcentrifugal force by spinning or rotating the wafer(s) on a turntable orcarousel, either about their own axis or about a common axis. Exemplaryspray processor machines suitable for adaptation in accordance with thepresent invention are described in U.S. Pat. Nos. 6,406,551 and6,488,272, which are fully incorporated herein by reference in theirentireties.

Spray processor type machines are available from TEL FSI, Inc. ofChaska, Minn., e.g., under one or more of the trade designations ORION™MERCURY™, or ZETA™. Another example of a tool system suitable foradaptation herein is described in U.S. Patent Publication No.2007/0245954, entitled BARRIER STRUCTURE AND NOZZLE DEVICE FOR USE INTOOLS USED TO PROCESS MICROELECTRONIC WORKPIECES WITH ONE OR MORETREATMENT FLUIDS; or as described in U.S. Patent Application PublicationNo. 2005/0205115, entitled RESIST STRIPPING METHOD AND RESIST STRIPPINGAPPARATUS or U.S. Patent Application Publication No. 2009/0280235,entitled TOOLS AND METHODS FOR PROCESSING MICROELECTRONIC WORKPIECESUSING PROCESS CHAMBER DESIGNS THAT EASILY TRANSITION BETWEEN OPEN ANDCLOSED MODES OF OPERATION.

Spray bar 120 comprises a plurality of nozzles to direct liquid ontowafer 113 in the form of a continuous stream or as liquid aerosoldroplets. The sulfuric acid solution is provided from liquid supplyreservoir 122 through line 123, and the stream of water vapor issimilarly provided from supply reservoir 124 though line 125. Phosphoricacid is provided from phosphoric acid supply reservoir 126 through line127 to sulfuric acid supply line 123. This configuration permitsaddition of phosphoric acid to the sulfuric acid solution with thebenefit that the phosphoric acid is not stored and heated in thepresence of sulfuric acid, and additionally that the amount ofphosphoric acid used in the treatment method may be independentlycontrolled from the amount of sulfuric acid as dictated by specificprocess requirements. Thus, a variable phosphoric acid concentration canbe applied during a treatment process as desired. Alternatively, thephosphoric acid can be supplied to the stream of water vapor at line125.

Spray bar 120 is preferably provided with a plurality of nozzles togenerate aerosol droplets of treatment composition that results fromimpinging the mixed acid liquid stream with the stream of water vapor.In a preferred embodiment, nozzles are provided at a spacing of about3.5 mm in spray bar 120 at locations corresponding to either the radiusof the wafer or the full diameter of the wafer when spray bar 120 is inposition over wafer 13. Nozzles may optionally be provided at differentspacing closer to the axis of rotation as compared to the spacing of thenozzles at the outer edge of the wafer. A preferred spray barconfiguration is described in U.S. Patent Application Publication No.2008/0008834, entitled BARRIER STRUCTURE AND NOZZLE DEVICE FOR USE INTOOLS USED TO PROCESS MICROELECTRONIC WORKPIECES WITH ONE OR MORETREATMENT FLUIDS.

A cross-sectional view of a spray bar 130 is shown in FIG. 4,illustrating a preferred nozzle configuration of the present invention.For purposes of the present invention, an integrally arranged set oforifices in a body that is directed to provide streams that impinge oneanother is considered a single nozzle. In the configuration as shown,acid liquid stream orifices 132 and 134 are directed inward to provideimpinging streams 142 and 144. Water vapor dispense orifice 136 islocated as shown in this embodiment between liquid acid solutionorifices 132 and 134, so water vapor stream 146 impinges with liquidacid streams 142 and 144 externally of the nozzle body. As a result ofthis impingement, atomization occurs, thereby forming liquid aerosoldroplets 148.

In addition, the droplets are given enhanced directional momentum towardthe surface of the substrate because of the relatively high pressure ofthe water vapor stream as it exits from water vapor dispense orifice136. This centrally located orifice in the nozzle assembly thus providesan advantageous directional aspect to assist in removal of material fromthe surface of the substrate. Alternatively, the positioning of theorifices may be reversed, i.e., the acid liquid stream may be dispensedfrom orifice 136 and water vapor may be dispensed from orifices 132 and134.

Optionally, an additional ingredient, such as a gas, may be dispensedfrom one or more orifices in the nozzle assembly.

The location, direction of the streams, and relative force of thestreams are selected to preferably provide a directional flow of theresulting liquid aerosol droplets, so that the droplets are directed tothe surface of a substrate to effect the desired treatment.

In one embodiment, the liquid aerosol droplets are caused to contact thesurface at an angle that is perpendicular to the surface of the wafer.In another embodiment, the liquid aerosol droplets are caused to contactthe surface of the wafer at an angle of from about 10 to less than 90degrees from the surface of the wafer. In another embodiment, the liquidaerosol droplets are caused to contact the surface of the wafer at anangle of from about 30 to about 60 degrees from the surface of thewafer. In an embodiment, the wafer is spinning at a rate of about 10 toabout 1000 rpm during contact of the aerosol droplets with the surfaceof the wafer. In another embodiment, the wafer is spinning at a rate ofabout 50 to about 500 rpm.

The direction of the contact of the droplets with the wafer may in oneembodiment be aligned with concentric circles about the axis of spin ofthe wafer, or in another embodiment may be partially or completelyoriented away from the axis of rotation of the wafer. System 110preferably employs suitable control equipment (not shown) to monitorand/or control one or more of fluid flow, fluid pressure, fluidtemperature, combinations of these, and the like to obtain the desiredprocess parameters in carrying out the particular process objectives tobe achieved.

FIG. 5 shows an example of a modified spray processing system 150 forcarrying out an aspect of the present invention, where liquid acidsolution is dispensed onto a substrate surface. In system 150, wafer153, as a particular microelectronic device for example, is supported ona rotatable chuck 154 that is driven by a spin motor 155. As above insystem 110, this portion of system 150 corresponds to a conventionalspray processor device. Liquid sulfuric acid solution is provided fromliquid supply reservoir 162 through line 163 to dispense orifice 170,which is configured to dispense a liquid acid stream onto the substratesurface. Phosphoric acid is provided from phosphoric acid supplyreservoir 166 through line 167 to sulfuric acid supply line 163. Thisconfiguration permits addition of phosphoric acid solution to thesulfuric acid solution with the benefit that the phosphoric acid is notstored and heated in the presence of sulfuric acid, and additionallythat the amount of phosphoric acid used in the treatment method may beindependently controlled from the amount of sulfuric acid as dictated byspecific process requirements. Thus, a variable phosphoric acidconcentration can be applied during a treatment process as desired.

A stream of water vapor is similarly provided from supply reservoir 164though line 165 to dispense orifice 172. Alternatively, the phosphoricacid can be supplied to the stream of water vapor at line 165. Dispenseorifices 170 and 172 may are configured so that the stream of liquidsulfuric acid composition and the stream of water vapor intersect priorto impinging the surface of the substrate. In an embodiment of thepresent invention, the dispense orifices 170 and 172 are moved togetherduring the treatment to scan across the surface of the substrate. In anembodiment of the present invention, lines 165 and 163 can be linked toform a two orifice nozzle array to assist in positioning control forscanning across the surface of the substrate.

In embodiments of the present invention, a gas inert to the particularspecies present in the treatment process, such as nitrogen gas, may bedirected at the reverse side of the wafer to modulate the wafertemperature and to promote etch uniformity. In a preferred embodiment, astream of gas is directed to the reverse side of the wafer correspondingto the primary impact area of the mixed acid liquid stream to provide alocalized offsetting cooling effect.

In one embodiment of the present invention, the substrate is pretreatedwith a pretreatment liquid, such as an acid pretreatment, that acts tomodify the surface characteristics of the substrate as desired. Forexample, the substrate may be pretreated with a dilute HF composition toremove any surface oxide that may have formed on the nitride.

In an embodiment of the present invention, a small amount of HF may beincluded in the mixed acid liquid stream or in the added water.Advantageously, the present process further comprising hot, dilute HF ina small amount, preferably less than 2%, more preferably less than onepercent based on total weight of liquid applied to the substrate, mayimprove the nitride etching rate and selectivity. Appropriate HFsolutions and species are described in U.S. Pat. No. 6,835,667, which isincorporated herein by reference.

Wafers are preferably heated to a temperature of at least about 90degrees C., either before, during or after dispensing of the treatmentcomposition. More preferably, wafers are heated to a temperature of fromabout 90 degrees C. to about 150 degrees C. In another embodiment, thewafers are heated to a temperature of from about 95 degrees C. to about120 degrees C. This heating can be carried out, for example, by heatingthe chamber using radiant heat, introduction of hot water or otherliquid solution to the wafer with substantial removal of the heatedliquid prior to application of the concentrated sulfuric acidcomposition, introduction of heated gases to the chamber, and the like.

In one embodiment, the wafers can be pretreated by submerging one ormore wafers into a bath of liquid, which may or may not be heated,quickly draining the contents of the bath (e.g. a “quick dump”procedure) and conducting the remaining treatment steps as describedbelow. The bath liquid can be, for example, DI water, DI watercontaining sulfuric acid, sulfuric acid/hydrogen peroxide mixture, aninert fluid (such as a fluorocarbon), sulfuric acid/ozone mixture, andthe like. This embodiment can provide substantial benefit in enhancingthroughput of the treatment process by more efficiently treating and/orheating the wafers. An example of a particularly suitable process systemthat can be used to employ this embodiment is the MAGELLAN™ systemcommercially available from TEL FSI, Inc., Chaska, Minn.

The method described above may be used to process multiple wafer-likeobjects simultaneously, as occurs with batches of wafers when beingprocessed in a spray-type processing tool such as the MERCURY™, or ZETA™spray processors commercially available from TEL FSI, Inc., Chaska,Minn., or the MAGELLAN™ system, also commercially available from TEL FSIInc., Chaska, Minn.

The present invention is preferably used in single wafer processingapplications where the wafers are either moving or fixed. The presentinvention permits selective removal of silicon nitride at a sufficientlyrapid rate to allow economical use of single wafer processing systems.The single wafer system affords superior control of the processingconditions of each wafer, and avoids damage to multiple wafers in theevent of catastrophic process failure, because only one wafer is treatedat a time.

The use of each of the described embodiments of the present invention asan intermediate process in an in-line wafer treatment process isspecifically contemplated as an embodiment.

The following examples illustrate the many embodiments provided above.The following etch data was collected with blanket silicon nitride films(Nitride) deposited using a horizontal furnace at a depositiontemperature of 820 degrees C. with no subsequent anneal. Films of SiGe50% were deposited at 475 degrees C. with no subsequent anneal. Films ofun-doped polycrystalline silicon (Poly) were deposited to a thickness ofabout 2000 Angstroms. All wafers were deglazed in order to remove nativeoxide. The deglaze process uses 100:1 HF (100 volume parts DI watermixed with 1 volume part 49 wt % HF) for 45 s (seconds) at roomtemperature (RT).

Examples 1-10 used a mixture of phosphoric acid and sulfuric acidcoupled with steam injection as a silicon nitride etching agent (labeledPhosSul+ in the examples below). The same PhosSul+ process conditionswere used in each example and are shown in Table 1 below.

Preheat/Pretreatment process conditions were varied in order to reduceor minimize the Poly and SiGe loss associated with the etching of thesematerials using the same PhosSul+ dispense conditions.

TABLE 1 PhosSul Dispense Conditions DH H3PO4 H2SO4 H3PO4 H2SO4 N2 DHBackside Dispense Flow Flow Temp Temp Steam Wafer Flow Height N2 FlowTime (s) (cc/min) (cc/min) (C) (C) Inject RPM (slm) (mm) (slm) Critical60 or 200 800 165 220 Yes 240 80 3.5 65 PhosSul+ 120 Process Variables

EXAMPLE 1

Nitride w/deglaze: H₂SO₄ Only Preheat/Pretreatment, followed by 60 sPhosSul+ Etch, resulted in an etch amount of 143.4 A (Angstroms).

EXAMPLE 2

Poly w/deglaze: H₂SO₄ Only Preheat/Pretreatment, followed by 60 sPhosSul+ Etch, resulted in an etch amount of 162.5 A. For the conditionsin Examples 1 and 2, the inventors observed an increased etch amount forPoly relative to Nitride.

Examples 1 and 2 used the Preheat/Pretreatment conditions of Table 2.

TABLE 2 Preheat/Pretreatment Dispense DH H2O2 H2SO4 H2O2 H2SO4 N2 DHBackside Dispense Flow Flow Temp Temp Steam Wafer Flow Height N2 FlowTime (s) (cc/min) (cc/min) (C) (C) Inject RPM (slm) (mm) (slm) Critical30 0 1000 RT 220 No 200 80 3.5 65 Pretreatment Process Variables

EXAMPLE 3

Nitride w/deglaze: SC-1, followed by H₂SO₄ Preheat/Pretreatment,followed by 120 s PhosSul+ Etch, resulted in an etch amount of 338.2 A.

EXAMPLE 4

Poly w/deglaze: SC-1, followed by H₂SO₄ Only Preheat/Pretreatment,followed by 120 s PhosSul+ Etch, resulted in an etch amount of 430.5 A.For the conditions in Examples 3 and 4, the inventors observed anincreased etch amount for Poly relative to Nitride.

Examples 3 and 4 used the Preheat/Pretreatment conditions of Table 3.

Examples 5-10, 11, and 12 used a mixture of sulfuric acid and hydrogenperoxide coupled with steam injection as an oxidizing agent (labeledViPR+ in the examples below).

TABLE 3 Preheat/Pretreatment Dispense DH H2O2 NH4OH H2O SC1 N2 DHBackside Dispense Flow Flow Flow Temp Steam Wafer Flow Height N2 FlowTime (s) (cc/min) (cc/min) (cc/min) (C) Inject RPM (slm) (mm) (slm)Critical 20 40 20 2138 70 No 600 150 6 0 Pretreatment Process Variables

EXAMPLE 5

Nitride w/deglaze: 30 s ViPR+ Preheat/Pretreatment, followed by 60 sPhosSul+ Etch, followed by 30 s ViPR+ Preheat/Pretreatment, followed by60 s PhosSul+ Etch, resulted in an etch amount of 308.0 A.

EXAMPLE 6

Poly w/deglaze: 30 s ViPR+ Preheat/Pretreatment, followed by 60 sPhosSul+ Etch, followed by 30 s ViPR+ Preheat/Pretreatment, followed by60 s PhosSul+ Etch, resulted in an etch amount of 11.8 A. For theconditions in Examples 5 and 6, the inventors observed an increased etchamount for Nitride relative to Poly, wherein a Preheat/Pretreatment stepincluding an oxidizing step, e.g., ViPR+ Preheat/Pretreatment, has beeninserted prior to dispensing a silicon nitride etching agent, e.g.,PhosSul+ Etch (two cycles of multi-step process).

Examples 5 and 6 used the Preheat/Pretreatment dispense conditions ofTable 4, e.g., ViPR+, before the first 60 s PhosSul+ dispense and againbefore the second 60 s PhosSul+ dispense.

TABLE 4 Preheat/Pretreatment Dispense DH H2O2 H2SO4 H2O2 H2SO4 N2 DHBackside Dispense Flow Flow Temp Temp Steam Wafer Flow Height N2 FlowTime (s) (cc/min) (cc/min) (C) (C) Inject RPM (slm) (mm) (slm) Critical30 85 850 RT 220 Yes 200 80 3.5 65 Pretreatment Process Variables

EXAMPLE 7

Nitride w/deglaze: 45 s ViPR+ Preheat/Pretreatment, followed by 120 sPhosSul+ Etch, resulted in an etch amount of 264.8 A.

EXAMPLE 8

Poly w/deglaze: 45 s ViPR+ Preheat/Pretreatment, followed by 120 sPhosSul+ Etch, resulted in an etch amount of 18.7 A. For the conditionsin Examples 7 and 8, the inventors observed an increased etch amount forNitride relative to Poly, wherein a Preheat/Pretreatment step includingan oxidizing step, e.g., ViPR+ Preheat/Pretreatment, has been insertedprior to dispensing a silicon nitride etching agent, e.g., PhosSul+Etch.

Examples 7 and 8 used the Preheat/Pretreatment conditions of Table 5.

TABLE 5 Preheat/Pretreatment Dispense DH H2O2 H2SO4 H2O2 H2SO4 N2 DHBackside Dispense Flow Flow Temp Temp Steam Wafer Flow Height N2 FlowTime (s) (cc/min) (cc/min) (C) (C) Inject RPM (slm) (mm) (slm) Critical45 85 850 RT 195 Yes 200 80 3.5 65 Pretreatment Process Variables

EXAMPLE 9

Nitride w/deglaze: 15 s ViPR+ Preheat/Pretreatment, followed by 120 sPhosSul+ Etch, resulted in an etch amount of 293.7 A.

EXAMPLE 10

Poly w/deglaze: 15 s ViPR+ Preheat/Pretreatment, followed by 120 sPhosSul+ Etch, resulted in an etch amount of 12.2 A [Observation ofnon-uniformity, wherein some wafers have areas that measure 55 A Polyetch due to incomplete oxidation during ViPR+ step.

Examples 9 and 10 used the Preheat/Pretreatment conditions of Table 6.

TABLE 6 Preheat/Pretreatment Dispense DH H2O2 H2SO4 H2O2 H2SO4 N2 DHBackside Dispense Flow Flow Temp Temp Steam Wafer Flow Height N2 FlowTime (s) (cc/min) (cc/min) (C) (C) Inject RPM (slm) (mm) (slm) Critical15 85 850 RT 205 Yes 200 80 3.5 65 Pretreatment Process Variables

Examples 11-16 used the same PhosSul+ process conditions and are shownin the Table 7.

TABLE 7 PhosSul+ Dispense Conditions DH H3PO4 H2SO4 H3PO4 H2SO4 N2 DHBackside Dispense Flow Flow Temp Temp Steam Wafer Flow Height N2 FlowTime (s) (cc/min) (cc/min) (C) (C) Inject RPM (slm) (mm) (slm) Critical60 200 800 165 220 Yes 240 80 3.5 65 PhosSul Process Variables

EXAMPLE 11

SiGe 30% w/deglaze: H₂SO₄ Only Preheat/Pretreatment, followed by 60 sPhosSul+ Etch, resulted in an etch amount of 275.2 A.

EXAMPLE 12

SiGe 30% w/deglaze: 45 s ViPR+ Preheat/Pretreatment, followed by 60 sPhosSul+ Etch, resulted in an etch amount of 33.1 A. The inventorsobserved a decreased etch amount of SiGe 30% when an oxidizing step hasbeen inserted prior to dispensing a silicon nitride etching agent.

Examples 11 and 12 used the Preheat/Pretreatment conditions of Table 8.

TABLE 8 Preheat/Pretreatment Dispense DH H2O2 H2SO4 H2O2 H2SO4 N2 DHBackside Dispense Flow Flow Temp Temp Steam Wafer Flow Height N2 FlowTime (s) (cc/min) (cc/min) (C) (C) Inject RPM (slm) (mm) (slm) Critical45 85 800 RT 220 Yes 200 80 5 30 Pretreatment Process Variables

EXAMPLE 13

SiGe 50% w/deglaze: H₂SO₄ Only Preheat/Pretreatment, followed by 60 sPhosSul+ Etch, resulted in an etch amount of 67.5 A.

EXAMPLE 14

SiGe 50% w/deglaze: 45 s ViPR+ Preheat/Pretreatment, followed by 60 sPhosSul+ Etch, resulted in an etch amount of 69.8 A.

TABLE 9 Preheat/Pretreatment Dispense DH H2O2 H2SO4 H2O2 H2SO4 N2 DHBackside Dispense Flow Flow Temp Temp Steam Wafer Flow Height N2 FlowTime (s) (cc/min) (cc/min) (C) (C) Inject RPM (slm) (mm) (slm) Critical45 85 800 RT 220 Yes 200 80 5 30 Pretreatment Process Variables

Examples 13 and 14 used the Preheat/Pretreatment conditions of Table 9.

Although only certain embodiments of this invention have been describedin detail above, those skilled in the art will readily appreciate thatmany modifications are possible in the embodiments without materiallydeparting from the novel teachings and advantages of this invention.Accordingly, all such modifications are intended to be included withinthe scope of this invention.

The invention claimed is:
 1. A method for selectively removing siliconnitride, comprising: providing a substrate having a surface with siliconnitride exposed on at least one portion of said surface and SiGe_(x),wherein x is greater than or equal to zero, exposed on at least anotherportion of said surface; dispensing an oxidizing agent onto said surfaceof said substrate to oxidize said exposed SiGe_(x); following saiddispensing said oxidizing agent, dispensing a silicon nitride etchingagent as a liquid stream onto said surface of said substrate to removeat least a portion of said silicon nitride; and repeating saiddispensing an oxidizing agent onto said surface of said substrate andsaid dispensing a silicon nitride etching agent as a liquid stream ontosaid surface of said substrate two or more cycles to selectively removea target amount of said silicon nitride.
 2. The method of claim 1,further comprising: prior to dispensing a silicon nitride etching agent,dispensing a heating agent onto said surface of said substrate topre-heat said substrate to a target temperature.
 3. The method of claim2, wherein said target temperature exceeds 150 degrees C.
 4. The methodof claim 2, wherein said dispensing said oxidizing agent and dispensingsaid heating agent are performed simultaneously.
 5. The method of claim1, wherein said dispensing said oxidizing agent includes exposing saidsubstrate to a mixture containing sulfuric acid and hydrogen peroxide.6. The method of claim 5, wherein said sulfuric acid is heated to atemperature in excess of 150 degrees C.
 7. The method of claim 5,wherein said sulfuric acid is heated to a temperature in excess of 200degrees C.
 8. The method of claim 5, wherein water is further added tosaid mixture of sulfuric acid and hydrogen peroxide.
 9. The method ofclaim 1, wherein said dispensing said oxidizing agent includes exposingsaid substrate to a mixture containing sulfuric acid and hydrogenperoxide in the presence of water vapor.
 10. The method of claim 9,wherein said mixture containing sulfuric acid and hydrogen peroxide isdispensed from a first array of injection openings located above saidsubstrate, and said water vapor is dispensed from a second array ofopenings.
 11. The method of claim 10, wherein said first array ofopenings and said second array of openings are oriented relative to oneanother to allow said mixture of sulfuric acid and hydrogen peroxide andsaid water vapor to mix in a space above said substrate.
 12. The methodof claim 11, wherein said first array of openings and said second arrayof openings are distributed radially along a spray arm that extendsabove said substrate from approximately a central region of saidsubstrate to approximately a peripheral region of said substrate. 13.The method of claim 12, wherein said substrate is rotated whiledispensing said mixture of sulfuric acid and hydrogen peroxide and saidwater vapor.
 14. The method of claim 1, wherein said dispensing asilicon nitride etching agent comprises dispensing phosphoric acid andsulfuric acid onto said surface of said substrate as a mixed acid liquidstream at a temperature greater than about 150 degrees C.
 15. The methodof claim 14, wherein said dispensing phosphoric acid and sulfuric acidremoves said silicon nitride at a rate in excess of 20 times greaterthan said oxidized, exposed SiGe_(x).
 16. The method of claim 14,wherein water is added to a liquid solution of said mixed acid liquidstream as or after said liquid solution of said mixed acid liquid streampasses through a nozzle.
 17. The method of claim 14, wherein saidsubstrate is rotated during the dispensing of the mixed acid stream. 18.The method of claim 14, wherein said mixed acid liquid stream is flowedonto said substrate in the form of a continuous stream or is sprayedonto said substrate in the form of liquid aerosol droplets.
 19. Themethod of claim 14, wherein: said phosphoric acid and sulfuric acid aremixed in a vessel for storage prior to dispensing from a nozzle as saidmixed acid liquid stream, or said phosphoric acid and sulfuric acid aremixed in-line at a location upstream from a nozzle to form said mixedacid liquid stream, or said phosphoric acid and sulfuric acid are mixedin a nozzle assembly prior to being ejected from a nozzle as said mixedacid liquid stream, or said phosphoric acid and sulfuric acid aredispensed as separate liquid solutions in the form of streams fromseparate orifices of a nozzle assembly, which separate streams thenimpinge and form said mixed acid liquid stream externally of the nozzleand prior to contact with said surface of said substrate.